Here is the function that would checking whether the given path is directory or not, using ftp_nlist;

ftp_file_list.php

<?php
function filecollect($conn_id,$dir='.') {
  static $flist=array();
  if ($files = ftp_nlist($cid,$dir)){
    foreach ($files as $file) {
      if (ftp_size($cid, $file) == "-1"){
        filecollect($cid,$file);
      } else $flist[] = $file;
    }
  }
  return $flist;
}
?>